Controllable pitch propeller



Jan. 21, 1941. "r, A. DlcKs 1 2,2291058 CONTROLLABLEl FITCH PROPELLER Filed April 29, 1937 s sheets-sheet 1 54ml zo ,T/zwwao" A. ickd Jan. 21, 1941. 1^, pms A' `2,229,058

CONTROLLABIJE PITCH PROPELLER Filed April 29, 1937 3 Sheets-Sheet 2 altar/WM;

Jan. 21, 1941. T ,1 DICKS 2,229,058

CONTROLLABLE PI-TCH PROPELLER Filed April 29, 1957 3 SheetS--Shet 3- nautics.

, viously employed speci-al pumps operatedby the Patented Jan. 21, 1941 UNITED STATE:

s PATENT vortica 2,229,058 ooN'rnoLLALE rrron PnoPELLEn f Thomas A. nicks, Pittsburgh, Pa. Application Apri129, 19st, serial No. 139.195

12 Claims.

The present invention relates to controllable pitch propellers, particularly as applied to aerocontrollable pitch propellers heretofore known in the art, are largely based upon three different principles of operation. These three types depend upon mechanical, electrical and hydraulic actuation respectively, for adjusting the propeller blades to the desired pitch.

' The mechanical type necessarily depends upon mechanical linkages from the stationary Vparts of the ship to the rotating hub. VDue to the relatively hi'gh speeds encountered and the large forcesv to be overcome, controlling mechanisms of this type soon become so badly worn that replacement with new equipment becomes neces.

sary. Moreover, the mechanical movements employed are in most cases so inherently heavy that their weight alone renders them undesirable and impractical.

Theelectrical types share a good many\ of .the disadvantages of the mechanical types. The usual devices of the electrical type, consist of an electric motor carried by the ub, the armature of which is directly connected through gearing to the blades which are to have ltheir pitch'adjusted. inasmuch as av high torque is requiredto over-` come the resistance of ythe blades to turning, a relatively large train of. these gears will be re# quired, resulting in undesirable weight and a correspondingly low speed of adjustment.

controllable pitch propelleis of the hydraulic type, have heretofore necessitated, in all known cases, pipe lines and other fluid 'connections exy 1 tending between the rotating propeller and the stationary portions of the ship. In some ,instances, hollow drive shafts have been usedfor conveying the oil or other fluid, but in every case hydraulic packing is required to seal the various rotatable joints and the danger of leakage is always present. Propellers of this type have preairplane power plant to produce the necessary `fiud pressure for obtaining adjustment of the blades. 'Refinements of this type of system, for example lthose for effecting an automatic control of the pitch of the blades, have required further modification and alterationof the equipment onP existing ships. Accordingly, it has been found to be impractical to attempt to .equip existing planes with pitch control mechanisms of this type as the4 expense involved is almost prohibitive. By the present invention, it is contemplated to combine the :advantages of known systems the i mechanlcaL'electrical and hydraulic types without introducing; their :inherent disadvantages. According to this invention, hydraulic pressure is employed for eectingthe desired variations in the pitch of the blades, andthe pump or pumps 5 for supplying this hydraulicpressure are built Y directly into the propeller hub, thus requiring no outside source of* pressure and accordingly no liuid conduitsbetween relatively moving parts and no Aappreciable modication of the ship itm self. The nature of the present construction! lends itself very readily .to automatic kcontrol and/or manu-al control from the cockpit of .the plane. The most convenient `manner for eilecting this control Iis by electrical devices Iutilizing as 15 source of current, .the battery ordinarily carried by the plane. It is also possible according to the construction of the present apparatus to vary the pitch of the vpropeller blades Whether or not the airplane engine is operating. Thus, even though' 20" a given engine may not be running, whether in the air or on the ground, its Yblades may ebe adjusted to any position to permitstarting of the engine, featheri'ng, or any other `effect dired.

Whereas it is highly important that independent control of the several propellers always be possible, the rinciple's of thepresent invention l render it feasible to so synchronize the propeller blades of a multi-motor airplane when desired, that all of the blades of all its propellers will assume the same pitch setting at any particular time. W

Briefly stated, the present invention comprises a hub containing a pluna'lityof propeller blades which are .adjusted through suitable gearingby an hydraulically operated piston.` The piston is in turn adjusted by actuation of sui-tablevalves4 which regulate the passage of fluid between the opposite ends of the piston and `a pump 0r pumps carried by ,the hub. The valves are set to their desired positions by electromagnetic means which may be energized automatically by centrifugal means carried by the hub, or manuallyFby selecting the position of one or morelswltches mounted in the cockpit of the plane. may be driven through suitable gearing by electromagnetic means also carried bythe hub, which is likewise energized automatically or manually as desired. The electromagnetic means for adjusting .the valves and-driving the pump is op 50 erable regar Aess of' Whetherthe power plant is running, rendering it possible to adjust Ithe blades to their starting pitch or to their feathering pitch, or to any/'intermediate pitch at any time. y

A more complete understanding of the present 55 The pump or pumps i teeth of one or more worm wheels orpinlons 82y invention will be had by a more complete description referring to the figures of the drawings.

In the drawings: Fig. 1 is a plan view, partly in section of the propeller hub; c

Fig. 2 is an elevation partly in section of th mechanism contemplated by the present invention and taken along line 2-2 of Fig. 4;

Fig. 3 is an elevation partly in section at right angles to the elevation of Fig. 2;

Fig. 41s a plan taken along lines 4-4 of Fig. 2; and

Fig. 5 is a circuit diagram showing the electrical connections.

`A three blade 4propeller hub is depicted in the drawings as comprising a body 28 provided with three blade sockets 22 `for reception of the root ends 24 of the blades 28. Whereas the present invention is equally applicable to propellers equipped with hollow or solid blades, the former type has been shown in the drawings, As particularly shown in Fig.. 1, the body of the h-ub is recessed at the base of each socket to provide a seat 28 for reception of'a bearing 38. A suitablebushing 32 -for cooperation with these bearings is ii-tted into the end .of each of the hollow blades. In addition to the usual bearings 34 surrounding the root end of the blade and carried by the socket, the present construction contemplates vthe provision of an annular gear 88 securely locked on the root ends of each oi' the blades. 'I'hese propeller bl-ades together with their bearings and gears are held in position in their respective sockets by means of the threaded rings 88 provided with suitable hydraulic packing 40. Cooperating with each of the annular gears 36, and shown as substantially parallel with the engine shaft 42, there are a sui-table number of rack bars 44 the movements of which operate upon the gears to effect-the desired movement of the blades to change their pitch.

As shown inFig. 2, the hub body 28 is assembled upon the nose 46 of an airplane, by means of a nose plate 48 which is bolted thereto, merely replacing the usual nose plate with which the particular ship is ordinarily equipped. The hub is splined at 45 to the engine shaft in the usual mariner and is provided with the customary bearing nut 50, collar 52, cone 84, split cone I8, bearing nut 58, and positioning ring 58.

The end of the hub nearest the engine, which is the endV shown in the lower part of Fig. 2, is provided with a counterbore 88 for reception of a portion of the control mechanism; Loosely mounted on the inner wall 82 defined by the counterbore, and supported upon one or more suitable bearings 84, there is provided an annular element 88 having a substantially cylindrical portion 88 provided on its periphery with a worm thread 10. This annular element is also provided with a flanged or circumferential portion 12, constituting in effect the rotor of an electrical machine. This circumferential portion may assume the form of al spider presenting a plurality of spaced poles. The outer wall 18 of the hub defined by the counterbore 88, suitably supports as by bolts orthe like, an annular or radially projecting element 18 carrying a suitable' winding or windings 88 to constitute what is in effect the stator of an electrical machine.

The worm 10 in assembled relations engages the which are secured to their separate shafts 84. These shafts carrying the pinions, are supported for rotation in suitable blocks 84 which are fastened by bolts 81 or otherwise secured in the counterbore 88 of the hub. These blocks are suitably bored to provide recesses 88 for the reception of shaft bearings 80 and 82 which serve to support the opposite ends of the shafts. The bearings 82 are assembled on the shaft by a nut 84 and the shaft and pinion assembly is held in the blocks by means of a nut 88 threaded into the block 88 so as to engage a race of the bearing 82, One end of .each shaft is extended beyond the bearing 98 and has secured thereto by a pin 88 or the like, an eccentric |80 which is received by a slotted yoke |02 integral with or secured to a piston |84. These pistons serve as pumping elements and operate in cylinders |88 formed by drilling directly into the' body of the hub at its suitably located protruded portions |08, After q these cylinders have been properly formed, they are closed to atmosphere at one end' by the insertion of threaded or otherwise attached plugs H0.

The operation of the pump may be summarized as follows: Under ordinary conditions when the windings 14 and 88 of the motor are not energized,

the friction between the worm 10 and the pinions 82 will cause the annular rings 88 to rotate with the hub of the propeller. The stator portion of the machine, 18 being rigidly afilxed to the hub will likewise rotate, and at the same speed as the rotor, When the windings are energized however, either automatically or selectively, to be described hereinafter, a torque will be set up between the stator andl rotor and there will be a differential movement causing rotation of the armature rotor. Naturally, this will drive the worm 10 causing it to rotate the pinions 82 and their shafts 84, carrying with themthe eccentrics |88 which operate in their respective yokes to drive the pumpv pistons |84. Y

After the hub body together with the control mechanism contained in its counterbore is mounted on the nose plate, the Joint between the hub body and the nose plate is provided with an annular thimble |05 which is threaded on to the nose plate and carries a suitable packing |81 to prevent the admission of dirt to the mechanism.

At these same enlarged or protruded portions |88 of the hub, a plurality of substantially radial bores are likewise formed to define fluid lpassages ||2 and ||4 which serve as intake and delivery conduits respectively for fluid subjected to pressure by the piston |04, which thus constitutes a iiuid pump. After the drilling operation has been completed, the pump intake and delivery passages are also provided with plugs ||8 to close them to atmosphere.

The upper end of the hub body as viewed in Fig. 2 is provided with a pair of annular counterbores |28 and |22 defining pump delivery and intake reservoirs respectively.` These reservoirs communicate with the radial delivery and intake passages already referred to, through longitudinally disposed passages |24, and |28 serving the delivery and intake sides of the pump respectively.

These passages |24 and |28 are enlarged or counterbored near their upper ends for the reception of spring pressed valves or check valves of other types for assuring the proper direction of the flow of liquid under the influence cf the pump. The delivery valve |28 and the intake valve |80 are suitablyseated to permit the passage of fluid in one direction only. Having formed the delivery and intake reservoirs, thecounterbores are closed v,

to atmosphere by annular rin'gs |32 and |34 respectively. which rings are preferably provided with tapered edges and tapered threads to as-.,

l sure their fluid tight relationship with the hub body.

A casing |33 containing a number of the control elements is superimposed upon the propeller hub body and fastened thereto by means of bolts |85 projecting from a plurality of lugs |36 extendingfrom the blade sockets 22. The casing is provided with-a base plate |38 which rests directly upon the upper portion of the hub body, and has extending upwardly therefrom .(as viewed in Figs. 2 and 3) a substantially cylindrical sleevev |40y Partially surrounding the sleeve |40, there is an outer cylindrical sleeve |42 which is jo-ined in fluid tight relationship to the base plate |38 by screw threads |44 or the like. In order to assure a fluid tight joint between the sleeve |40 and its surrounding sleeve |42, a threaded thimble |43 is screwed on to the sleeve |40 vand bears with aY tapered surface |45 against a similar or dissimilar taper formed on the upper end of the sleeve |42. Between `the opposed concentric walls of the sleeves |40 and |42, there is positioned an annular piston |46, the movements of which are subjectA to control by the application of uid pressure to its surfaces, VThe oppositesurfaces of this' piston are provided with suitable annular hydraulic packings |48 to prevent fluid leakage as far as possible. appropriate retainers |49. Projecting upwardly from the propeller hubs and directly fastened to thev piston, are theends of therack bars 44 `each formed with a reduced end |50 to define a shoulder |52 between which and the nut |54, the piston is tightly clamped. Thus it will be seen, that when the piston is operated to move upwardly or downwardly, the rack bars will follow, such movements being in turn Vtransmitted to the vannular gears 38 to impart a corresponding movement to the propeller blades and thus adjust their pitch.

The supply of fluid tothe surfaces of this piston is controlled by a pair of piston valves |56 and |58 which are1 operated together by a yoke |60,

which is in turn fastened, shown as riveted, up-

on a sleeve |62 which is slidably mounted upon a 'rod |64. The rod |64 extends downwardly through' the yoke and at its reduced lower end threadedly carries a perforated piston |68 which is bathed in fluid |10 so as to constitute a dash pot to damp the actuation of the centrifugal control mechanism lto be described. Suitable provision may be made for varying the apertures in the piston |68 so as to change the degree of retardation. Cylinders for these valve and dash pot pistons are deiined by a web |12 extending across the base of the casing |33. In the central portion of this web, the dash pot cylinder |14 is deflned, beyond which and diametrlcally disposed,

are the valve cylinders |16 and |18 for reception of thevalves |56'and |58 respectively. A packing nut surrounds the rod |64 to close the upper end of Vthe cylinder |14 into which it is threaded. This nut is provided with a` suitable hydraulic packing |82 which may be held inposition by a retainer |84;

As more clearly shown in Fig. 2 of the drawings, each ofthe piston valves is providedwith three ports. The valve |56 and its cylinder |16 are provided with an upper port |86 in communication with the pump intake reservoir through a pipe connection |81; a central port |88 having a pipe connection |80 to a port |92 opening to the lower surface of the piston |46; and a lower port |94 having a pipe connection |86 to the delivery reservoir of the' pump. The valve These packings may be positioned by port 208 and pipe connection 204 to the central |58 and its cylinder |18 are provided with corresponding ports, comprising an upper port |88 communicating through a connection 200 with the pump delivery reservoir; a central port' 202 communicating through a pipe 204 and a conduit 206 formed in the wall of the member |40, with a port 208 servingthe upper surface of the, piston |46; and a lower port -2'I0 connected through a pipe 2|2 with the intakereservoir of the pump.

. Since 4the hydraulic operation in the present case, preferably depends upon a full system, a well 2 I4 is provided to depend from the base plate |38 and lextend down into the hollow engine shaft. This `wellris closed by `a plate 2|6 threaded thereinto ush with the upper surface of the base plate. This well communicates through a passage 2 8 formed in one of the walls of the web |12 with some point of the hydraulic system, indicated for convenience as being the intake side of the pump. A piston 220 mounted in the well is provided with a hydraulic packing 222 andits retainer 224, and is subjected to the force of a relatively strong spring 226 which seats upon the lower end of the well. This assembly thus tends to maintain the entire hydraulic system at a uniform, pressure so that itwill be maintained full at all times. In the event that the lquantity of fluid should become depleted `through leakage or .any othercause, one of the many plugs in the system, such'as the plugs ||0 and H6, can be removed and additional fluid un'der pressure admitted to refill the system and the well 2|4. It is also comtemplated to'apply pressure fittings to the system through which additional fluid may 3- be admitted by a` vsocalled quick connector coupling. l

As shown in Figs. 2 and 3, the annular piston |46 is in its lowered position. l When it is desired to raise the piston to change the pitch of the propeller blades, the valves |56 and |58 together with their yoke |60 will be lowered, admitting fluid from the delivery side of the pump through the port |94 of valve |56 into the chamber formed by the reduced portion of the valve and through the port |88 and pipe connection |80 to the port |62 thus tending to force the piston to its raisedv position. At the same time, fluid is withdrawn from the upper lsurface' of the piston through the port 202 of the `valve |58 into the chamber formed by the reduced portion of the valve and out through the lower port 2 I0 and pipe connection 2|2 to the intake pump reservoir. When the annular piston is vin its upper position and it is desired to lower it, the piston valves |56 and |58 together with their yoke |60 will be raised and the operation just described willbe reversed to apply the delivery from the pump or pumps to ,j the upper surface o f the piston and withdraw 60 the fluid from the lower surface.

In vorder to effect the raising and lowering of the valve to accomplish the results just described, a pair ,of solenoids 228 andv230, carried by a frame '232. controlan armatureor plunger 234 65 carried bv the sleeve |62 and positioned thereon so as to move simultaneously therewith. The solenoid frame 232 is provided with a pair of legs 228 which rest upon the web |12 and the frame is suitablvsecured in this position` as by a ring 238 suitably received in a grooved portion of the sleeve |40. In order to assure the assumption of a neutral position by the valves |56 and |58 and,

the plunger`234 carried by the rod- |64, upper and 'Lf lower balancing springs 24| and 243 respectively, 75

' drical sleeve |40, a. pair or normally open switches `the circuit is as follows:

will be lifted electromagnetioally to raise the yoke |60 with the valves |56 and |58 causing the pumps to force the annular piston |46 to its lower position. Similarly when the solenoid 2301 is energized, the armature or plunger 234 will be drawn downwardly, carrying with it the sleeve |62, yoke |60 and valves |56 and |56, resulting in the pumps forcing the annular piston |46 to its upper position. It will be noted that the solenoids are provided with a common lead 240,

vwhile the upper solenoid terminates in the lead 242 and the lower solenoid terminates in a lead 224. These leads may be combined into a suitable multi-conductor cable which is carried down through the casing |33 into the hub body 20 where they are suitably connected with the circuits of the windings 14 and 80 of the motor and to brushes 246, 248 and 250. These brushes bear upon collector rings 252, 254 and 256 carried by the nose plate 48 whence they are carried through conductors 258, 260 and 262 respectively and through a suitable cable to the cockpit of the plane. The circuits will be traced more explicitly in conjunction with the explanation of Fig. 5

of the drawings.

Mounted in the upper portion of the cylin- 266 and 268 are provided designed to be closed under the pressure of an arm 210 carried by a ily ball governor mechanism 212. The governor assembly is mounted on the reduced upper end of the rod |64, as by a nut 213, and bears against the shoulder 236. The governor comprises a lower block 214 to which are pivoted a pair of lower arms 216 and 21B whose upper ends are pivoted to the Weights 280 and 282 respectively. An upper pair of arms 264 and 286, which may be provided with a spring 281 of' the customary type, are also pivcted to the weights 280 and 282 respectively, and these upper arms are in turn pivoted about a common axis by a pin or the like 288 passing through an opening formed in a plate 290 which may be seated on a suitable shoulder 292 formed near the upper end of the sleeve |40. The upper end of the sleeve may be closed by a vcap 294 threaded or otherwise attached thereto.

Referring now to Fig. 5, a switch arm 304 provided in the cockpit of the plane, is provided with a plurality of contacts 306, 308.and 3|0. The

switch arm is also connected through the battery 3|2 customarily carried by the plane and thence to ground 3|4. The motor 14-80, which has been shown for convenience as a shunt motor, but which'may assume any other desirable form, likewise has one of its terminals connected to ground 3|4. When it is desired to shift the pitch of the blades in one direction, the switch arm 304 is moved to its contact point 306 whereupon From ground 3|4 through battery 3`|2 through switch arm 304 to switch contact 306, by way of conductor 244 to energize solenoids 230 causing a lowering of the plunger 234, then through lead 240 -and through the motor `to ground 3|4. It will thus' be seen,`

that when the solenoid 230 is energized to move the plunger 234, the motor will be simultaneously energized to assure operation of the pump.

If it is desired to adjust the pitch of the blade in the other direction, the contact arm 304 will be moved to contact 3|0 whereupon the circuit may be traced as follows: From ground 3|4 through battery 3|2 through switch arm 304 and its contact 3|0, then through conductor 242 to energize the upper solenoid 226, whereby the plunger will be pulled to its raised condition, then through conductor 240 to the motor and again to the ground. Here again when the upper solenoid is energized, the motor is likewise energized and the valve adjustment will occur simultaneously with the operation of the pump.

The central contact 308 for the switch arm 304, is connected through a lead 3|6 common to the switches 266 and 268, which are actuated by the arm 210 of the fiy ball governor mechanism. The opposite side of switch 266 is connected through a conductor 3|8 lwith the lower solenoid 230 through the conductor 244. The other pole of the switch 268 is connected by a lead 320 with the conductor 242 and consequently the upper solenoid 228. Hence it will be seen, that when the switch arm 302 is moved to the central or automatic position so as to make contact with the point 308, operation of the fly ball governor will automatically shift the pitch of the blades in accordance with the instantaneous speed at which the propeller is driven.' Assuming the switch arm 304 to b e in contact with the point 308, and the y ball governor raised s0 as to close the switch 266, the circuit will be as follows:

From ground 3|4 through battery 3|2 and switch arm 306, through contact 308, lead 3|6, through the switch 266 to lead 3|8, through co'nductor 244 to energize the solenoid 230, then through the lead 240 and the motor to ground Should the engine speed become suiiiciently reduced for the contact arm 216 to close the switch 268, still assuming the switch arm 304 to rest upon contact 308, the circuit will be as follows: From ground 3|4 through battery 3|2, switch arm 304, contact 308, lead 3|6, switch 266 and lead 320 to energize `solenoid 228 then through conductor 240 and the motor again to ground 3| 4.

In order that there will be no fluttering and to avoid constant shifting when the pitch is being conti olled automatically, the dash pot which has already been described is provided.

I claim:

1. A controllable pitch propeller comprising a hub supporting a plurality of blades, a piston articulated to said blades to vary their pitch, a' cylinder receiving said piston, a pump carried by said hub to supply fluid pressure to said piston, a fluid connection between said pump and said piston, and means completely carried by said hub for driving said pump, said means receiving its basic source of energy from a point inboard of said propeller and independently of the rotation of said propeller, said means and said piston being disposed on opposite sides of a plane passing through the axes of said blades.

2. A controllable pitch propeller comprising a hub supporting a plurality of blades, a piston articulated to said blades to vary their pitch, a cylinder receiving said piston, a pump carried by said hub to supply fluid pressure to said piston, a iiuid connection between said pump and said piston, electromagnetic means completely carried by said hub for driving said pump, said electroliti yau

dit

accepts magnetic means and said piston being disposed on opposite sides of a plane passing through the axes of said blades.

3. A controllable pitch propeller comprising a hub supporting a plurality of blades, a piston articulated to said blades to vary their pitch, a pump having inlet and outlet ports carried by said hub to supply uid pressure to said piston, shiftable valve means between each of said ports and said piston for controlling the direction of application of said fluid pressure to said piston, and` electromagnetic means carried by said hub for positively shifting said valve means.

4i. A controllable pitch propeller comprising a hub supporting a plurality of blades, a piston articulated to said blades to vary their pitch, a cylinder receiving said piston, a pump carried by said hub to supply iiuid pressure to said piston, said pump having inlet and outlet ports, a fluid connection between said pump and said piston, valve means for controlling said ports and directing said uid pressure, and interconnected means for shifting said valve means and for driving said pump.

5. A controllable -pitch propeller comprising a hub supporting a plurality of blades, a piston articulated to said blades to vary their pitch, a

pump carried by said hub to supply uid pressure to said piston, said pump having inletand outlet ports, valve means for controlling said ports and directing said fluid pressure, and interconnected electromagnetic means for shifting said valve means'and for driving said pump.

6. A controllable pitch propeller comprising a hub supporting a plurality of blades, a piston articulated tolsaid blades to vary their pitch, a pump carried by said hub to supply fluid pressure to said piston, shiftable valve means ior selectively directing said fluid pressure to opposite sides of said piston, and centrifugal governing means carried by said hub for shifting said valve means and for controlling operation of said pump.

7. A controllable pitch propeller comprising a hub supporting a plurality of blades, means subjected to fluid pressure connected to said blades to vary their pitch and electrically driven means and an electric driving means therefor carried by said hub and completely rotatable therewith for producing said fluid pressure, said means being disposed on opposite sides of a plane passing through the blade axes.

8. A controllable pitch propeller comprising a hub supporting a plurality of blades, a piston `connected with said blades for varying their pitch, a closed system in said hub containing a a body of liquid in said hub contacting opposed surfaces of said piston, a plurality of pumps carried by said hub for shifting liquid from one surface of the piston to the other and a prime `mover completely carried by said hub for driving said pumps, said prime mover and said piston being disposed on opposite sides of a plane passing through the blade axes.

10. A controllable pitch propeller comprising a hub supporting a plurality of blades, a closed hydraulic system and a prime mover' therefor completely carried by said hub, means driven by said prime mover for applying pressure to said system to vary the pitch of said blades and positively actuated reversible valve meansinterposed in said system for reversing the effect of said pressure upon said blades, said prime mover receiving energy from a source carried inboard of said propeller` and independently of the rotation of said propeller. y

ll. A controllable pitch propeller comprising a hub supporting a plurality oi blades, a closed hydraulic system and driving means therefor completely carried by said hub, and means carried by said hub disposed on opposite sides of a plane passing through the blade axes cooperating with said driving means for applying pressure to said system when said propeller is idle for varying the pitch of said blades, said' driving means receiving its basic source of energyirom a point inboard of said propeller.

12. A controllable pitch propeller comprising a hub supporting a plurality of blades, a closed hydraulic system and driving means therefor completely carried by said hub, and means carried by said hub disposed on opposite sides of a plane passing through the blade axes cooperating with said driving means for applying pressure to said system when said propelleris rotating for varying the pitch of said blades, said driving means re- THOMAS A. DICKS. 

